This invention relates to radio frequency communication systems and more particularly to systems for transmitting and receiving multi-channel information over pairs of independent sidebands using multiple FM subcarriers, with a minimum of interchannel distortion.
The prior art has seen many systems for transmitting radio signals by means of subcarriers. In general, the number of signals which may be transmitted is a function of the accuracy with which frequency selection may be accomplished for the subcarriers and the sidebands. In general it is quite difficult to arrange subcarrier sidebands adjacent one another without leaving a substantial frequency range to eliminate overlap between sideband signals.
For example, U.S. Pat. No. 3,518,376 to Cayman and Walker discloses a system in which a plurality of single sideband audio modulated subcarrier signals are superimposed on an FM broadcast signal. As that patent demonstrates, heretofore the individual subcarrier signals are FM single sideband and are widely spaced in order to eliminate interference between channels. For this reason the number of information channels in a given bandwidth is drastically reduced.
It is an object of the present invention to provide a radio frequency communication system employing closely spaced dual independent sideband AM modulation of multiple FM subcarriers with a minimum of interchannel distortion.
It is another object of this invention to provide new transmitter and receiver designs to enable the use of dual independent sideband AM modulation of multiple FM subcarriers.